In a letter to Portland Mayor Charlie Hales and Police Chief Mike Marshman, the ACLU of Oregon warns that if the city targeted the organizers of Portland's anti-Trump marches for arrest, they may have violated the protesters' constitutionally protected freedoms.

They also noted that police officers involved may not be exempt from civil litigation if that proves to be the case.

"Despite clear law to the contrary, PPB appears to be engaged in a pattern and practice of retaliatory arrest of local organizers," ACLU of Oregon legal director Mat dos Santos says in the letter. "We have received other reports of well-known organizers and activists being targeted by PPB for arrest during peaceful protests and are investigating those allegations."

"While we continue to evaluate the facts, we caution PPB that it is a violation of the rights of the protesters arrested if police actions are motivated by a desire to chill speech and law enforcement actions would 'chill or silence a person of ordinary firmness from future First Amendment activities,'" Dos Santos writes.

McKelvey earlier today released a statement accusing the mayor of having him arrested for refusing to participate in Hales' now-canceled March of Hope—an accusation denied by spokesmen for the police and the mayor's office.

"The mayor, as police commissioner, does not have the authority to direct Portland Police to arrest anyone," says Hales spokesman Brian Worley. "People are arrested for breaking laws. To claim the mayor would, or could, target and arrest people for political retaliation is not only completely inaccurate, it is dangerous."

The ACLU's full letter is below:

November 22, 2016

Dear Mayor Hales and Chief Marshman,

Last night, we learned that Portland Police Bureau (“PPB”) arrested Gregory McKelvey, Kathryn Stevens, and Micah Rhodes, members of PDX Resistance and well-known organizers. Targeting individuals for arrest for constitutionally protected speech is prohibited by law.

PDX Resistance organizers were singled out for arrest despite engaging in activities similar to peaceful protesters in their vicinity. From our view, the only distinguishing characteristic is their role as leaders in other recent protests that were publicly opposed by your offices.

An arrest made in retaliation for a person’s exercise of protected speech violates the First Amendment. While we continue to evaluate the facts, we caution PPB that it is a violation of the rights of the protesters arrested if police actions are motivated by a desire to chill speech and law enforcement actions would “chill or silence a person of ordinary firmness from future First Amendment activities.” Unlike most other courts, the Ninth Circuit has held that a First Amendment retaliation claim can lie even if the arrest is supported by probable cause. If a First Amendment retaliation claim can be established, then officers would likely not be entitled to qualified immunity.

Despite clear law to the contrary, PPB appears to be engaged in a pattern and practice of retaliatory arrest of local organizers. We have received other reports of well-known organizers and activists being targeted by PPB for arrest during peaceful protests and are investigating those allegations.

Not only is retaliatory arrest unconstitutional, it is wasteful, consuming limited law enforcement resources in pursuit of charges prohibited by law. For example, activist Teressa Raiford was acquitted after an arrest last year for similar activities. The ACLU of Oregon filed an amicus brief in her case and successfully showed the court that the state has a high burden when wielding the criminal law against protesters engaged in protected First Amendment activity.

While we understand the difficulties faced by local law enforcement, silencing the voices of community leaders through a practice of harassing arrests is clearly unconstitutional and destroys trust between the community and its public servants.

As those selected to serve the community, we urge you to ensure that public speech, including protest, is protected and not punished.